In an HVAC system having an under floor air plenum, cool or warm air is supplied to the plenum below the floor of an occupied space to be cooled or heated. In order to cool or heat the occupied space above the floor, modular terminals with diffuser grilles are mounted in the floor at predetermined locations to allow the cool or warm air in the plenum to flow into the occupied space above the floor. The terminals are located and oriented to accommodate the configuration of the occupied space to be cooled or heated.
Typically the floor terminal includes a basket mounted in the floor of an occupied space for delivering air from the under floor air plenum to the occupied space above the floor through a diffuser grille. In some installations, the modular floor terminal basket includes a stationary round basket and rotatable internal round basket. Both the stationary basket and the rotatable basket have openings in their sides and bottoms. Rotation of the internal basket within the stationary basket opens and closes the openings thereby controlling the amount of air that flows through the terminal basket, through the diffuser grille, and into the occupied space. The internal rotatable basket is connected to the diffuser grille so that rotation of the diffuser grille opens and closes the openings and thereby controls the amount of air flowing through the floor terminal. Walker U.S. Pat. No. 6,361,432 discloses a modular floor terminal with a stationary basket and a rotatable basket connected to the diffuser grille.
In certain cooling applications, it is advantageous to have a diffuser grille that diffuses the cooled air in a low velocity horizontal swirl pattern that remains tight to the floor as the cooling air from the under floor plenum displaces the air in the occupied space. The low velocity cooling air mixes slowly with the air in the occupied space rising slowly as the heat load from people and equipment is absorbed. H. Krantz-TKT GmbH has manufactured and sold at a metal horizontal diffuser grille shown in FIGS. 1-3. While the Krantz diffuser grille has enjoyed success in the marketplace, the weight and cost of the Krantz horizontal diffuser grille has limited its acceptance and competitiveness in the marketplace.